1. Field
The presently disclosed subject matter relates to an optical deflector apparatus which can be applied to a vehicle headlamp, for example.
2. Description of the Related Art
A prior art two-dimensional optical deflector is constructed by a mirror, a movable frame surrounding the mirror for supporting the mirror through a pair of torsion bars, inner piezoelectric actuators (first piezoelectric actuators) of a torsion-bar type fixed between the movable frame and the torsion bars and serving as cantilevers for rocking the mirror through the torsion bars with respect to an X-axis of the mirror, a support body surrounding the movable frame, and outer piezoelectric actuators (second piezoelectric actuators) of a meander type fixed between the support body and the movable frame and serving as cantilevers for rocking the mirror through the movable frame with respect to a Y-axis of the mirror perpendicular to the X-axis (see: JP2009-223165A).
Generally, the mirror is rocked with respect to the X-axis for a horizontal deflection at a high frequency by the inner piezoelectric actuators using sinusoidal waves, while the mirror is rocked with respect to the Y-axis for a vertical deflection at a low frequency by the outer piezoelectric actuators using straight-type saw-tooth waves.
When the above-described prior art two-dimensional optical deflector is applied to a vehicle headlamp for distributing light, since each of the saw-tooth waves are not symmetrical with respect to the center thereof, i.e., a rising period or a falling period of each of the saw-tooth waves is much longer than a falling period or a rising period thereof, a light source must be turned off to stop the horizontal deflection for the falling period of each of the saw-tooth waves, which would complicate the control. Also, since the saw-tooth waves are of a straight-type, irregularity of illumination would occur. This will be discussed later in detail.